Electromagnetic driving mechanism for oscillating displacement pumps

ABSTRACT

Electromagnetic driving mechanism for oscillating displacement pumps (10) is described which comprises a linear motor (21, 22) and a control circuit (51, 52, 53, 54). The control circuit controls the stroke movement of the linear motor (21, 22) in response to the deviation of the actual value of a stroke parameter (stroke distance, stroke speed, stroke acceleration, and pressure of the medium being pumped) from the reference value of this stroke parameter. A preferred embodiment is assembled in such a manner that the pump (10) proper may be easily exchanged and constructed as a discardable unit. Such a pump unit (10) is particularly desirable in connection with blood pumps.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on German Patent Application Ser. No. P2,823,802.0, filed in the Federal Republic of Germany on May 31, 1978and on the corresponding application PCT/DE79/00053 filed on May 31,1979. The priority of the original German filing date is claimed.

BACKGROUND OF THE INVENTION

The invention relates to a driving mechanism for oscillatingdisplacement pumps. Such driving mechanisms are known from British Pat.No. 1,442,500. In these known driving mechanisms the time sequence ofthe volume flow and of the suction pressure as well as of the dischargepressure is determined by the geometry of the pole shoes and of thefield configuration. Thus, among others, the flow speed is alsodetermined.

When conveying media which can withstand only a certain reduced pressureor increased pressure without damage, it is necessary to reduce thedriving speed of such pumps so that the occurring reduced or increasedpressures do not exceed the permissible limit values. Thus, the massflow is substantially reduced and the pump is insufficiently utilized.However, it is possible to reduce these difficulties by using volumestorage means in the form of expansion chambers arranged upstream ordownstream, whereby the entire pumping system becomes more involved andmore expensive. Besides, by these features it is not excluded that thepermissible reduced or increased pressures are exceeded anyway.Additionally, these features cause an increase in the volume of themedium being conveyed in the pump conveying system.

In connection with media to be conveyed which may not be exposed tocertain maximum shearing stresses, it is necessary to keep theacceleration forces of the moving pump components so low that the limitvalue of the shearing stress is not exceeded at any points of thehydraulic system. This also reduces the degree of efficiency of thepump.

It is known in connection with positioning means for disc memories inthe data processing art, which comprise electro-dynamic linear motors,to provide a control circuit which controls the positioning stroke inresponse to the difference between the actual value of the positioningdisplacement and the reference value of the desired position as well asin response to the positioning speed. However, in connection with suchpositioning means for disc memories used in the electronic dataprocessing art, problems of quite a different type occur. Especially, itis essential that the desired reference position is reached precisely sothat this known device could not provide any hints with regard todriving mechanisms for oscillating displacement pumps ("Feinwerketechnikand Mikronik", Vol. 77, Nr.4 1973, pages 151 to 157).

OBJECTS OF THE INVENTION

Thus, it is the object of the invention to construct the above mentioneddriving mechanism in such a manner that on the one hand the permissiblelimit values for the reduced pressure, the increased pressure, theacceleration and so forth, are maintained with certainty while on theother hand the largest possible conveying capacity is achieved withinthe limit values.

SUMMARY OF THE INVENTION

The invention has achieved the above objectives in an electromagneticdrive mechanism for an oscillating displacement pump, including a statorand a runner which is guided by the stator and movable across the fieldlines of the stator, and further including a coupling device between thestator and the runner on the one hand, and between the stator and thedisplacement pump on the other hand, said stator comprising a permanentmagnet system for producing the stator field and said runner comprisinga runner winding which is characterized by a control circuit arrangementwhich comprises at least one first signal pick-up for providing a signalrepresenting the actual or measured value of a stroke parameter by atleast one reference second pick-up for providing a signal representing areference value of a stroke parameter, by at least one comparatoroperatively connected with its two inputs to said first and secondpick-ups, and which is further characterized in that said runner windingis connected to the output of the comparator through a closed loopcontroller member and, if desired, through a direction reversing switchand through a power output amplifier, whereby the current in said runnerwinding is controlled during the movement of said runner winding when itis performing a stroke.

A driving mechanism according to the invention in which the signalpick-up is a displacement transducer, makes possible the utilization ofthe driven displacement pump as a dosing pump. If the signal pick-upprovides a signal which depends on the speed for example in a transducerfollowed by a differentiating circuit or speed transducer, the drivendisplacement pump is especially suitable for conveying of media, such asblood, which are sensitive relative to high shearing stresses. If thesignal pick-up is a pressure transducer, it is possible to avoidexceeding a predetermined excess pressure and/or to avoid that thepressure falls below a predetermined reduced pressure. Thus, the drivendisplacement pump is especially suitable for pressure sensitive media orfor media which tend to degas. If the reference value pick-up e.g. 2speed pick-up is connected to two end position value pick-ups for thetwo reversing circuits of the runner, it is possible to keep the pumpfrequency constant while the conveying speed is variable. This featureis especially advantageous for using the driven pump as a blood pump.

If the runner is guided along the pole core of a correspondingly shapedstator, a rather simple longitudinal guiding of the runner isaccomplished which uses components which are present anyway. If thisguiding means is constructed with anti-friction bearings, a low frictionguiding is accomplished which thus has a low dissipation loss.

The assembly of the mechanism results in a very compact unit comprisingthe driving mechanism and the displacement pump. The present couplingmechanism according between the motor and the pump provides anespecially stiff coupling device having a high strength and an efficientmaterial utilization of the components. Further, the assembly of thedisplacement pump with its drive means is much simplified and so is itsmaintenance. Besides, in this way it is possible to exchange the sameparts for one another. The present displacement pump with its drive isuseful for many purposes for example for conveying, especially difficultmedia such as strongly adhesive media or media which are aggressiverelative to conventional sealing means or media which are sensitiverelative to the sealing means. The present pump may be manufacturedrelatively cheaply of a material suitable for many purposes. Where it isdifficult to remove media or where high requirements regarding thecleanliness of the pump component must be satisfied, for example,germ-free requirements when the pump is used as a blood pump, the pumpcomponent may be treated as a disposable part without any substantialcosts. In an embodiment of the driving mechanism and of the displacementpump according to certain aspects of the invention it is easy toassemble the two pump components and to also disassemble the pumpcomponents again. Thus, treating the pump component as a disposable partis possible.

BRIEF FIGURE DESCRIPTION

The invention will be explained in the following with reference to anexample embodiment shown in the drawings of a driving unit with anoscillating displacement pump and with reference to several controlcircuits for the driving unit, wherein:

FIG. 1 shows a partially schematic vertical section through a drivingmechanism and a bellows pump according to section line I--I in FIG. 2;

FIG. 2 is a top plan view onto the mechanism according to FIG. 1, withthe upper yoke disc removed;

FIGS. 3 to 6 illustrate block circuit diagrams of different controlcircuits for the mechanism according to FIGS. 1 and 2; and

FIG. 7 is a circuit arrangement of the block schematic according to FIG.6.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BESTMODE OF THE INVENTION

The oscillating displacement pump shown in FIGS. 1 and 2 comprises abellows pump 10 and an electromagnetic driving mechanism 11 forming mainstructural groups.

The bellows pump 10 is constructed as a pump with an internalthroughflow. The pump comprises a folding bellows having a cylindricalshape which merges at both of its facing ends into a respective smooth,vaulted annular cover member 13 or 14. In the center of the covermembers 13 and 14 there is joined without any seam a hose member 15 or16. At the transition between the cover member 13 and 14 and therespective hose member 15 and 16 there is an annular bulge 17 or 18which extends in the radial direction beyond the axially adjacentmembers. Thus, a ring groove 19 or 20 is formed between the ring bulge17 and 18 and the respective cover member 13 or 14.

The folding bellows 12, the two cover members 13 and 14, the adjacent,connected hose members 15 and 16, and the ring bulges 17 and 18 areformed as a single piece of a rubber elastic material, for example, ofpolyethylene or polyvinylchloride.

The valves necessary for a continuous conveying of a medium through thepump are not shown in FIG. 1. These valves may be constructed either aspassive valves, for example, as spring loaded check valves which may beconnected by means of hose nipples to the hose members 15 and 16 andwhich are operated by the flowing medium itself, or these valves may beconstructed as active valves, for example, as electromagneticallyoperated hose valves which are arranged outside the hose members 15 and16 and which are externally effective on the hose members as so-calledpinch cocks or pinch valves.

The electromagnetic driving mechanism 11 comprises a stator 21 and arunner 22. The stator comprises two permanent magnet systems 23 and 24for producing the magnetic stator field. Both permanent magnet systemsare constructed as hollow cylinder shapes as shown in FIG. 2. The twopermanent magnet systems 23 and 24 are made of an aluminum nickel cobaltalloy. The ring shape of the hollow cylinder of the permanent magnetsystem 23 and 24 is interrupted on the right-hand side in FIGS. 1 and 2by a respective opening 27 extending through in the radial and axialdirection. The opening 27 is bounded by plane wall surfaces arranged inparallel relative to each other.

The magnetic fields of the two permanent magnet systems 23 and 24 arealigned to oppose each other.

A circular, ring shaped pole shoe 25 is located between the twopermanent magnet systems 23 and 24. The permanent magnet systems 23 and24 abut on the axial facing surfaces of the pole 25. A cylindrical polecore 26 having a circular cross-section is arranged centrally within thepole shoe 25 and the permanent magnet systems 23 and 24. A ring shapedpole gap of uniform gap width is provided between the ring shaped poleshoe 25 and the cylindrical pole core 26. The pole core 26 has the sameaxial length as the sum of the axial extensions of the pole shoe 25 andof the two permanent magnet systems 23 and 24. A circular yoke disc 28or 29 is located at each of the two ends of the pole core. The yoke disc28 located at the top in FIG. 1 is formed as an individual componentwhich is screwed to the pole core 26. The lower yoke disc 29 forms anintegral part with the pole core 26. It may also be contemplated thatboth pole discs are made as individual components and screwed to thepole core or that the pole core is divided about at its longitudinalcenter and that the pole discs are formed as an integral part at eachend of the pole core.

The ring shaped pole shoe 25, the pole core 26, and the two yoke discs28 and 29 are made of a soft magnetic, ferro-magnetic material, forexample, of an iron cobalt alloy. The axial extension of the pole shoe25 and of the pole core 26 are adjusted relative to each other andrelative to the axial extension of the two permanent magnet systems 23and 24 in such a manner that in the assembled condition of these partsthere is no air gap between the parts.

The runner 22 is made as a non-ferro-magnetic body which comprises awinding 31 and a winding carrier 32. The winding carrier 32 is made of asleeve 33 and of two end discs 34. The sleeve 33 has the shape of a thinhollow cylinder. The two end discs 34 have a circular ring shape and aradially outwardly extending extension, each of which forms a cantileverarm 35 of the runner 22.

The axial extension of the pole shoe 25, of the stator 21, and the axialextension of the winding 31 of the runner 22 as well as the largeststroke of the runner 22 that may occur in operation, and thus thebellows pump 10 are so adjusted relative to one another that the axialextension or length of the winding 31 is at least approximately equal tothe sum of the axial extension or length of the pole shoe 25 and of thelargest possible operational stroke of the runners 22. The largestoperational stroke is, as a rule, predetermined by the requirements tobe satisfied by the bellows pump 10. The axial length or extension ofthe pole shoe 25 results primarily from the magnetic characteristics ofthe components participating in the generation of the stator field,whereby the axial length of the windings 31 is then also determined. Dueto this dimensioning, all turns of the winding 31 dip at least once intothe radial stator field in the pole gap between the pole shoe 25 and thepole core 26 when the runner 22 executes a full stroke. None of theturns runs along completely idle without ever participating in the powergeneration of the driving mechanism 11 and without merely causing energylosses.

The runner 22 is guided along the pole core 26 by means of two groups ofanti-friction bearings 36, whereby each group comprises threeanti-friction bearings 36 which are uniformly distributed about thecircumference of the runner 22 as shown in FIG. 2. One anti-frictionbearing group is arranged at each one of the facing sides of the windingcarrier 32. The inner races of the anti-friction bearings 36 are locatedon bearing pins 37a which in turn are inserted in small bearing bucks37b. These bearing bucks 37b are screwed down on the outwardly facingfacing ends of the two end discs 34 by means of screws not shown. Theouter races of the anti-friction bearings 36 run directly on thecircumferential surface of the pole core 26. The cantilever arms 35 arepart of a coupling device 38 between the bellows pump 10 and its drivingmechanism 11. A bail 39 forms a further part of the coupling device 38and is constructed as a cylindrical rod having a circular cross-section.This rod shaped bail 39 is inserted into a respective circular throughhole in the cantilever arms 35, wherein it is respectively clamped tightby means of a respective radially extending clamping slot 40 or 41 and aclamping screw not shown, but screwed-in in the circumferentialdirection. A connecting plate 42 is clamped to the bail 39 as a furtherpart of the coupling device 38 again by means of a clamping slot 43 anda clamping screw not shown. Thus, the connecting plate 42 may easily beadjusted on the bail 39 with reference to the dimensions of the pumpbellows 12 and relative to the expansion condition of the latter in thestarting position of the runner 22 of the driving mechanism 11. Theconnecting plate 42 comprises at its end facing away from the bail 39 afork end 44. This fork end 44 is adjusted in its dimensions to thedimensions of the ring groove 19 at the upper end of the folding bellows12 in FIG. 1. A second connecting plate 45 forms a further component ofthe coupling device 38 and is screwed to the yoke disc 29 located at thelower end. The connecting plate 45 also has a forked end 46 facing awayfrom the yoke disc 29. The forked end 46 is also adjusted, just as theforked end 44 of the connecting plate 42, to the dimensions of the ringgroove 20 at the lower end of the folding bellows 12.

As indicated in FIG. 2 and as more clearly seen in FIG. 1, the foldingbellows 12 of the bellows pump 10 is assembled with the drivingmechanism 11 in such a manner that the forked end 44 of the connectingplate 42 engages into the ring groove 19 at the upper end of the foldingbellows 12 and the forked end 46 of the connecting plate 45 engages inthe ring groove 20 at the lower end of the folding bellows 12. Thecoupling device 38 transmits the stroke movements of the parts of thedriving mechanism 11 which are movable relative to each other, to thebellows pump 10. This is so because of the axial engagement of theforked end 44 of the connecting plate 42 and the parts of the foldingbellows 12 on both sides of the ring groove 19, namely, the cover member13 and the ring bulge 17, and because of the axial engagement of theforked end 46 of the connecting plate 45 with the parts of the foldingbellows 12 adjacent to the ring groove 20, namely, the cover member 14and the ring bulge 18.

As may be seen from FIG. 1, the rod shaped bail 39 extends upwardlybeyond the cantilever arm 36. A sliding spring 47 is secured to thisupwardly extending end. The sliding spring 47 rests against a slidingresistor 48 and slides back and forth on the sliding resistor inresponse to the stroke movement of the bail 39. The sliding resistor 48is secured in a manner not shown, in a fixed position relative to thestator 21 of the driving mechanism 11. The sliding spring 47 and thesliding resistor 48 form a signal pick-up, namely, a displacementtransducer 49 forming part of a control circuit arrangement 51, 52, 53or 54 which will be explained in the following with reference to FIGS. 3to 6.

The control circuit arrangement 51 shown in FIG. 3 serves as adisplacement or stroke control of the driving mechanism 11 and thus ofthe bellows pump 10.

The control circuit arrangement 51 shown in FIG. 3 comprises in additionto the displacement transducer 49, a reference value pick-up orgenerator 55 for the reference displacement of the runner 22, acomparator 56, a closed loop control member 57 including a proportionalintegration controller and a power output amplifier stage 58. The ratedor reference value generator 55 produces a displacement time signal andthe runner 22 is intended to follow with its stroke movement, saiddisplacement time signal. The output of the displacement transducer 49and of the reference value generator 55 are connected to the two inputsof the comparator, however, with signs (polarities) opposing each other.The comparator forms a sum representing signal from the two inputsignals. The output of the comparator 56 is connected to the input ofthe closed loop controller and the output of the latter is connected tothe input of the power output amplifier 58. The power output amplifierprovides an adjustment signal to the winding 31 of the runner 22connected to the output of the power output amplifier.

The control circuit 52 shown in FIG. 4 serves for controlling thepressure in closed loop fashion in the bellows pump 10 and/or in theconnected hydraulic system. The control circuit 52 comprises in additionto the displacement transducer 49 a pressure transducer 60, one each ofa reference value generator 61 or 62 for the rated pressure at each ofthe two movement directions of the runner 22, one each of an endposition value pick-up 63 or 64 for the two reversing positions of therunner 22 and a comparator 65. The control circuit 52 further comprisesa direction reversing switch 66, a second comparator member 67, and aclosed loop control member 68 including a proportional integrationcontroller and an output power amplifier stage 69 as described above.

The output of the displacement transducer 49 is connected to the signalconductor input of the comparator 65. In addition, the output of each ofthe two end position value pick-ups 63 and 64 is connected to thecontrol conductor inputs of the comparator 65. The output of thecomparator 65 is connected to the control input of the directionreversing switch 66. The outputs of the two reference value generators61 and 62 are connected to the signal conductor inputs of the directionreversing switch 66. The output of the latter and the output of thepressure transducer 60 are connected, with opposite signs (polarities)to the two inputs of the further comparator member 67. The output of thefurther comparator member 67 is in turn connected to the input of theclosed loop control member 68 and the output of the latter in turn isconnected to the input of the power output amplifier stage 69 which alsoprovides a control signal to the winding 31 of the runner 22.

The control circuit 53 shown in FIG. 5 serves for the closed loop speedcontrol of the driving mechanism 11. With a supplementing feature thiscontrol circuit 53 also serves for the closed loop acceleration controlof the driving mechanism 11.

The control circuit 53 comprises in addition to the displacementtransducer 49 a differentiating circuit 70, one each of a referencevalue generator 71 or 72 for the reference or rated speed in each of themovement directions of the runner 22, one each of an end position valuepick-up 73 or 74 for the two reversing positions of the runner 22, acomparator 75, a direction reversing switch 76, a comparator member 77,a closed loop control member 78 with a proportional integrationcontroller, and a power output amplifier stage 79. The output of thedisplacement transducer 49 is connected to the input of thedifferentiating circuit 70 and to the signal conductor input of thecomparator 75. The output of each of the two end position value pick-ups73 and 74 is connected to the control conductor inputs of the comparator75. The output of the latter is connected to the control conductor inputof the direction reversing switch 76. The outputs of the reference orrated value pick-up 71 and 72 are connected to the signal conductorinputs of the direction reversing switch 76. The signal conductoroutputs of the latter, as well as the output of the differentiatingcircuit 70 are connected, with opposite signs (polarities) to the inputsof the comparator member 77. The output of the latter is connected tothe input of the closed loop control member 78 and the output of thelatter is connected to the input of the power output amplifier stage 79.The latter supplies the winding 31 of the runner 22 with a controlsignal required for the closed loop speed control or regulation.

If in the control circuit arrangement 53 described above a seconddifferentiating member 80 is connected between the differentiatingmember 70 and the comparator members 77, the output signal of the seconddifferentiating member 80 corresponds to the second differentiation ofthe displacement signal relative to time. Thus, this signal correspondsto the measured signal of the acceleration of the runner 22 of thedriving mechanism 11. If the two rated value pick-up or generators 71and 22 are adjusted so that each delivers a respective rated valuesignal for the acceleration in one of the two motion directions of therunner 22, the thus modified circuit arrangement 53' operates as aclosed loop control circuit for the acceleration of the drivingmechanism 11.

The control circuit arrangement 54 shown in FIG. 6 serves for the closedloop control and thus for the maintaining of a constant stroke frequencyof the bellows pump 10 and of its driving mechanism 11 while the strokespeed is varying. The control circuit 54 comprises in addition to thedisplacement transducer 49 a differentiating circuit 81, a rated valuegenerator 82 for the rated or reference speed in the two directions ofmotions of the runner 22. The control circuit 54 further comprises anend position value pick-up or transducer 83 or 84 for each of the tworeversing positions of the runner 22, a comparator 85, a directionreversing switch 86, a comparator member 87, a closed loop controlmember 88 including a proportional integration controller, and a poweroutput amplifier stage 89. The output of the displacement transducer 49is connected to the input of the differentiating circuit 81 andsimultaneously to the signal conductor input of the comparator 85. Theoutput of the reference or rated value pick-up or generator 82 isconnected on the one hand to the signal conductors input of thedirection reversing switch 86 and on the other hand to each of a controlconductor inputs of each of the two end position value pick-ups 83 and84. The output of the latter is connected to each of the controlconductor inputs of the comparator 85. The outputs of the latter isconnected to the control conductor input of the direction reversingswitch 86. The signal conductor output of the switch 86 and the outputof the differentiating circuit 81 are in turn connected, with oppositesigns (polarities) to the inputs of the comparator circuit 87. Theoutput of the latter is connected to the input of the control member 88and the output of the control member 88 is connected to the power outputstage 89 which supplies the winding 31 of the runner 22. Due tosupplying the output signals of the speed reference value 82 also to thecontrol conductor inputs of the end position value pick-ups 83 and 84,the end position limiting values of the stroke are respectivelydisplaced in response to a change in the stroke speed of the drivingmechanism which may occur for any reason. Thus, a longer stroke isperformed when the stroke speed is higher and vice versa. As a result,the stroke frequency of the entire oscillating system remains constantwithin certain limits of the stroke and thus of the speed.

For elucidating the circuit diagrams of one of the control circuits 51to 54 the circuit diagram of the last discussed control circuit 54 isexplained in more detail with reference to FIG. 7.

The differentiating circuit 81 comprises an operational amplifier 91including a resistor 92 and a capacitor 93 in a negative feedbackcircuit. The resistor 92 and the capacitor 93 are connected in parallelto one another. A series circuit comprising a resistor 94 and acapacitor 95 is connected to the negative input of the operationalamplifier 91. Due to the resistor 92 in the negative feedback circuitand due to the capacitor 95 in the input circuit, the operationalamplifier 91 acts as a differentiating circuit. The resistor 94 and thecapacitor 93 cooperate with the operational amplifier as a low passfilter.

The comparing circuit 87 comprises an operational amplifier 96 with aresistor 97 forming a negative feedback circuit. The negative input ofthe operational amplifier 96 is connected to two resistors 98 and 99connected in parallel to each other. The signal conductor output of thedifferentiating circuit 81 is connected to the resistor 98 and thesignal conductor output of the direction reversing switch 86 isconnected to the resistor 99. Thus, the comparator provides a sum signalbased on the two input signals.

The control member 88 comprises an operational amplifier 101 including anegative feedback circuit comprising a resistor 102 and a capacitor 103connected in series. The negative input of the operational amplifier 101is further connected to a resistor 104 which in turn is connected to theoutput of the comparing circuit 87. Due to this circuit arrangement, theoperational amplifier 101 has simultaneously a proportional as well asan integrating transmission function or characteristic.

The power output stage 89 comprises two complementary transistors 105and 106 which operate as a push-pull current amplifier in the A-B typeof operation.

The direction reversing switch 86 comprises an operational amplifier 110with a negative feedback circuit including a resistor 111. The negativeinput is further connected to a resistor 112. The positive input isconnected to a resistor 113. The positive input of the operationalamplifier 110 is further connected to the drain terminal of a fieldeffect transistor (FET) 114. The source terminal of the field effecttransistor 114 is connected to ground. The gate electrode of the fieldeffect transistor 114 forms with the series resistor 115 the controlconductor input of the direction reversing switch 86. The output of thecomparator 85 is connected to the just mentioned control conductor inputof the direction reversing switch 86. Depending upon the output voltageof the comparator 85, the reference value of the speed appears at theoutput of the direction reversing switch with a positive or a negativepolarity.

The end position pick-up 83, 84 comprises an operational amplifier 115'including a negative feedback circuit with a resistor 116 connected inparallel to a field effect transistor 117. The gate electrode of thefield effect transistor 117 is connected through a series resistor 118to the output voltage of the comparator 85. The negative input of theoperational amplifier 115' is further connected to a resistor 119 whichin turn is connected to the output of the reference value pick-up orgenerator 82 for the speed. Depending on the output voltage of thecomparator 85, one or the other end position value of the displacementtransducer 49 appears at the output of the end position value pick-upsor generators 83, 84. In this context, the end position value isproportional to the reference speed due to the connection of thereference value pick-up or generator 84 for the speed to the resistor119 and to the control conductor input of the end position value pick-upor generator 83, 84.

The comparator 85 comprises two operational amplifiers 121 and 122. Theoperational amplifier 121 comprises in its negative feedback circuit aresistor 123. A resistor 124 is connected to the negative input of theoperational amplifier 121. The resistor 124 forms the signal conductorinput of the comparator 85 and the output of the displacement transducer49 is connected to this signal conductor input of the comparator 85.Additionally, a resistor 125 is connected to the negative input of theoperational amplifier 121 and to a voltage divider 126. The output ofthe first operational amplifier 121 is connected to the negative inputof the second operational amplifier 122, the positive input of whichforms the control conductor input of the comparator 85 and is connectedto the outputs of the end position value pick-up or generator 83, 84.Due to the circuit arrangement of the first operational amplifier 121,the latter supplies a sum signal representing the output signal of thedisplacement transducer 49 and the output value of the voltage divider126, to the second operational amplifier 122. The second operationalamplifier 122 constitutes the comparator portion proper and supplies adirection dependent control signal. The starting position for the strokemovement of the runner 22 may be adjusted at the voltage divider 126 atthe negative input of the first operational amplifier 121.

As far as nothing else has been said above, it is to be assumed that thepositive input of the described operational amplifiers is connected toground.

We claim:
 1. An electromagnetic drive mechanism for providing acontrolled back and forth driving movement, comprising stator meansincluding magnet means for providing respective stator magnetic fields,runner means, support means supporting said runner means for a linearback and forth displacement relative to said stator magnetic fields,runner winding means (31) operatively carried by said runner means,whereby said runner winding means interact with said stator magneticfields during the movement of said runner means, a closed loop controlcircuit operatively connected to said runner winding means forcontrolling said driving movement, said closed loop control circuitcomprising sensing means for sensing an instantaneous measured value toprovide a corresponding first electrical signal representing aninstantaneous parameter of said runner means, reference signal means forproviding a second electrical signal representing a rated value,comparator means having a first input connected to said sensing meansand a second input connected to said reference signal means forcomparing said first and second electrical signals with each other, andcontrol circuit means connecting an output of said comparator means tosaid runner winding means for supplying a comparator output controlsignal to said runner winding means whereby the control of said runnermeans takes place during any displacement driving and within said backand forth movement.
 2. The mechanism of claim 1, further comprisingoscillating pump means, connecting means for securing said oscillatingpump means to said runner means, end position sensing means connected tosaid closed loop control circuit for sensing return point positions ofsaid runner means to provide respective electrical return signals tosaid closed loop control circuit, and direction reversing switch meansalso connected to said closed loop control circuit for reversing thedirection of displacement of said runner means.
 3. The mechanism ofclaim 2, comprising further comparator means having three inputs, saidsensing means having an output connected to said first mentionedcomparator means and to one input of said further comparator means, saidend position sensing means comprising two sensors connected to therespective other inputs of said further comparator means, said directionreversing switch means being connected to an output of said furthercomparator means to said reference signal means and to said firstmentioned comparator means for providing said control signal for saidrunner means.
 4. The mechanism of claim 3, wherein said reference signalmeans comprise two reference signal sources both of which areoperatively connected to said direction reversing switch means forproviding a reference signal for each direction of movement of saidrunner means.
 5. The mechanism of claim 3, further comprising electricalconductor means operatively connecting said reference signal means toboth of said end position sensors and to said direction reversing switchmeans.
 6. The mechanism of claim 1, wherein said sensing means forsensing an instantaneous measured value comprise displacement sensingmeans for measuring an electrical signal corresponding to theinstantaneous displacement or distance travelled by said runner means.7. The mechanism of claim 6, wherein said displacement sensing meanscomprises a potentiometer resistor (48) and a sliding spring contact(47) connected to said runner means for adjusting said sliding springcontact along said potentiometer resistor (48).
 8. The mechanism ofclaim 6 or 7, further comprising differentiating circuit means (70, 81)operatively connected between the displacement sensing means (49) andsaid comparator means (77) for providing a signal representing theinstantaneous speed of said runner means.
 9. The mechanism of claim 8,wherein said differentiating circuit means comprise two differentiatingmembers (70, 80) connected in series between the displacement sensingmeans and the comparator means (77) for providing a signal representingthe acceleration of said runner means.
 10. The mechanism of claim 1,wherein said sensing means for sensing an instantaneous measured valuecomprise a pressure transducer (60) connected to said comparator means.11. The mechanism of claim 1, wherein said sensing means for sensing aninstantaneous measured value connected to said comparator means is avelocity sensor.
 12. The mechanism of claim 1, wherein said controlcircuit means in said closed loop control circuit comprise an integralcontroller member for integrating a control signal.
 13. The mechanism ofclaim 1, wherein said control circuit means in said closed loop controlcircuit comprise a proportional integral control member forproportionally integrating a control signal.
 14. The mechanism of claim1, wherein said control circuit means in said closed loop controlcircuit comprise a proportional integral differential control member forproportionally integrating and differentially a control signal.
 15. Themechanism of claim 1, wherein said stator means comprise an annular,closed pole shoe and a pole core arranged centrally therein, saidsupport means of said runner means (22) comprising guide means forguiding the runner means along the pole core (26).
 16. The mechanism ofclaim 15, wherein said runner guide means comprise two groups of guidemembers each group comprising three anti-friction bearings (36), oneeach of the anti-friction bearing groups being arranged at each end ofthe runner means so that said anti-friction bearings (36) run directlyon the pole core (26).
 17. The mechanism of claim 15 or 16, wherein saidmagnet means of said stator means comprise two permanent magnet systemsincluding hollow cylinders with aligned slots, said mechanism furthercomprising cantilever arm means (35) connected with said runner means(22), said cantilever arm means extending at right angles to themovement path of said runner means (22) and through said slots (27)aligned in parallel to said movement path of the runner means (22), saidcantilever arm means (35) being connectable to a movable member (13) tobe driven.
 18. The mechanism of claim 17, wherein said cantilever armmeans comprise two cantilever arms (35), each of which is rigidlyconnected substantially to a respective end of said runner means (22)and each of which extends through a respective one of said slots of theadjacent permanent magnet system cylinders (23, 24), said runner meansfurther comprising a rod (39) for rigidly connecting both cantileverarms (35) to each other outside said stator means (21), said rod (39) inturn being connectable with a movable member to be driven.
 19. Themechanism of claim 1, further comprising pump means and plug-in typeconnection means operatively arranged between said pump means and saidmechanism, said pump means comprising a stationary part connected tosaid stator means and a movable part connected to said runner means foroperating said pump means by the movement of said runner means.
 20. Themechanism of claim 19, wherein said pump means comprise a bellows pump(10) having a stationary end connected to said stator means and amovable end connected to said runner means.
 21. The mechanism of claim20, wherein said bellows pump (10) comprises at each of its two ends(13, 14) a reduced diameter portion (19, 20) between two larger diameterportions (13, 17, 14, 18) extending in both axial directions from therespective reduced diameter portions.
 22. The mechanism of claim 21,wherein the reduced diameter portion is constructed as an all aroundgroove (19, 20) and the adjacent larger diameter portions areconstructed as all around bulges (17, 18).
 23. The mechanism of claim19, wherein said plug-in type connection means (42, 45) each comprise afork type end (44, 46) for holding said pump means.